A recent meta-analysis in BMJ on the association between baldness and coronary heart disease has gotten a lot of press (see NYT and Boston Globe). Looking at the comments section for these articles you can see that some readers are jokingly conflating this association with causality:

OK that’s it, I’m getting a hairpiece.

or are pointing to possible mediators:

Considering that drugs such as Rogaine increase the risk of coronary problems, maybe the increase in risk is due in part to the drugs men take to combat the hair loss.Or perhaps balding men are stressed out about their hair.

It’s interesting to see how scientific research gets filtered through mass media, and how the public reacts to and interprets that filtered information. Jorge Cham of PhD comics satirises that process here:

But back to the news flash that got me going on this tangent. Risk factors are important to identify. Some risk factors actually cause the illness, while some risk factors share a common cause with an illness. If we are concerned with detecting the presence of an illness, whether a risk factor also causes the illness may not be a primary concern. It is helpful to know who is at a greater risk for different illnesses, especially if early detection can help improve the health outcome. For example, if a bald person knows that baldness is a risk factor for heart disease this may induce them to avoid the possible causes of heart disease that they can control.

As for baldness and its sequalae, at this point I am only willing to conclude that baldness has a causal association with a year-round preference for hats.